Process for controlling pulp chip deterioration with kraft green liquor

ABSTRACT

THIS INVENTION RELATES TO A TREATMENT USED TO CONTROL THE DETERIORATION OF PULP CHIPS DURING OUTDOOR STOCK PILING FOR LONG PERIODS OF TIME. THE TREATMENT INVOLVES A SPRAYING OR DIPPING OF THE PULP CHIPS WITH A KRAFT GREEN LIQUOR WHICH IS A MIXTURE OF SODIUM SULFIDE AND SODIUM CARBONATE IN WATER. THE TREATMENT GREATLY REDUCES THE LOSS OF WOOD SUBSTANCE OVER LONG PERIODS OF OUTDOOR STORAGE. THE LOSS OF WOOD SUBSTANCE IN WOOD CHIPS WITH THE TREATMENT IS APPROXIMATELY ONE-THIRD OR LESS THAN THAT WITHOUT THE TREATMENT.

United States Patent Office 3,646,196 PROCESS FOR CONTROLLING PULP CHIPDETERIORATION WITH KRAFT GREEN LIQUOR Edward L. Springer and Wallace E.Eslyn, Madison, Wis., assiguors to the United States of America asrepresented by the Secretary of Agriculture No Drawing. Filed Apr. 29,1970, Ser. N0. 33,074 Int. Cl. A01n 11/00, 11/06 US. Cl. 424-162 1 ClaimABSTRACT OF THE DISCLOSURE This invention relates to a treatment used tocontrol the deterioration of pulp chips during outdoor stock piling forlong periods of time. The treatment involves a spraying or dipping ofthe pulp chips with a kraft green liquor which is a mixture of sodiumsulfide and sodium carbonate in water. The treatment greatly reduces theloss of wood substance over long periods of outdoor storage. The loss ofwood substance in wood chips with the treatment is approximatelyone-third or less than that without the treatment.

A nonexclusive, irrevocable, royalty-free license in the inventionherein described, throughout the world for all purposes of the UnitedStates Government, with the power to grant sublicenses for suchpurposes, is hereby granted to the Government of the United States ofAmerica.

BACKGROUND OF THE INVENTION (1) Field of the invention This inventionrelates to the stock piling of pulp chips with particular reference to atreatment for reducing the deterioration of wood substance duringstorage.

(2) Description of prior art In general, outside storage of pulp chips,introduced in the early l950s, resulted from the need to stock pilechips produced from residues of saw mills and veneer plants. When theeconomic advantages of handling wood as a bulk material became apparent,many mills introduced chipping of logs and stock piling of the chips asan alternative to log storage.

With the increased use of this method of handling wood, it becameapparent that there were disadvantages as well as advantages in usingthis method. One of the primary disadvantages is the loss in woodsubstance during long periods of chip storage because of fungal action.The average loss is about 1 percent per month in wood substance althoughlarge variations in this figure have been noted. Pulp yields from thesechips are not greatly affected although exceptions are found usuallyafter long storage. Kraft pulping is usually not affected but tall oilyields tend to be low. In sulphite pulping, chip storage generallyresults in lower pulp brightness with increased bleaching costs.

The most obvious difference between log and chip storage is that chippiles tend to heat up. Temperatures of 140 to 150 F. are not uncommon. Awide range of temperatures can be found in various parts of the pilewith the result that thermophilic, thermotolerant, and mesophilicmicroorganisms can exist in the pile simultaneously. Heat production iscaused by enzymatic respiration of the wood cells, microbial oxidation,and chemical oxidation. Temperatures rise rapidly in the pile reaching amaximum in about 2 weeks, remain high for several months depending onthe size of the pile, and then decline gradually to ambient temperature.

3,646,196 Patented Feb. 29, 1972 A chemical treatment used to preventchip deterioration must meet the following criteria. First, it must beeffective for a considerable length of time and the cost must bereasonable in relation to the losses incurred from chip deterioration.Second, it must be compatible with the pulping process, must not causepollution, and must not be toxic to personnel. The chemical treatmentmust reduce the heat buildup in the stock piled pulp chips and preventthe growth of micro-organisms if loss in wood substance is to bereduced.

SUMMARY In general, the principal improvement of this invention residesin a chemical treatment to control degradation of pulp chips. A chemicaltreatment comprising an aqueous mixture of sodium sulfide and sodiumcarbonate, hereafter called kraft green liquor, was found to substantially reduce loss of wood substance in pulp chip storage. The kraftgreen liquor solution is made by simply dissolving the sodium sulfideand sodium carbonate in water by any means available. The treatment ofthe pulp chips can be accomplished by spraying, dipping, or by any othermeans available to get the solution on to the chips. The treatment levelis determined by the uptake of the treating solution and the percentageof sodium sulfide and sodium carbonate in the solution.

Accordingly, an object of this invention is to provide a treatment tocontrol degradation of chips during outdoor storage. Another o'bject ofthis invention is the provision of a treatment that will inhibit boththe growth of micro-organisms and the production of heat in the stockpile of pulp chips. A further object of this invention is the provisionof a chemical treatment which is economical, simple, and quick ascompared to mechanical treatments for controlling degradation of pulpchips.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In further illustration of thisinvention the following examples are given:

Example I The influence of the kraft green liquor on the release ofinitial heat of fresh wood chips was studied by placing the chips in aninsulated box and observing the temperature profiles at the center ofthe samples. The boxes, constructed of polystyrene foam, have aninternal volume of 3.9 cubic feet with a wall thickness of 8 /2 inches.The inside dimensions of the insulated box are 22 /2 by 13 /2 by 22inches. Each box is fitted with air inlet and outlet manifolds and wasfed water-saturated air at ambient temperature at a measured rate,Thermocouples placed in the center of the chip pass and on the outsideWall were used to measure the temperatures. Because temperature profilesof untreated chips can not be satisfactorily duplicated, presumablybecause of changes in the wood with time, untreated control samples wererun with every treated sample.

The kraft green liquor solution used contained 7.7 percent sodiumcarbonate and 1.9 percent sodium sulfide. The treatment level,determined by uptake of the treating solution, was 2.1 pounds of sodiumcarbonate and 0.51 pound of sodium sulfide per pounds of ovendried wood.

Fresh aspen chips of 53 percent moisture content by weight were treatedby submerging them for 10 minutes in the test solution and draining for2 hours before placing them in the insulated boxes. For each box withtreated samples, there was a box of control samples treated with waterinstead of the test kraft green liquor solution.

When the chips were submerged in the green liquor solution, anexothermic reaction occurred that raised the 3 temperature of the chipssomewhat higher than ambient. The reaction is believed to be caused byhydrolysis of esterlinkages and neutralization of the carboxy groups bythe base.

The treated and untreated control chips were kept in their insulatedboxes 27 days. The air rate to each box was 1.4 cubic feet per day. Whenplaced in the test box, the temperature in the center of the treatedchip mass was 80 F. During the test period this temperature graduallydecreased to 78 F. Ambient temperature during this time averaged 74 F.with a variation of less than 2 F. The temperature at the center of thewater-soaked sample, or the untreated, was initially at 66 F., rose to84 F. in 8 days, to 85 in 13 days, and then gradually decreased to 80 F.Thus, little or no heat was evolved by the green liquor treated samples,whereas considerable heat was evolved by the untreated control samples.Although treatment with green liquor caused an immediate exothermicreaction on contact with the chips, it apparently also stopped thenatural heat evolving process.

After 27 days in an insulated box, the control chips were covered withfungal growth and had a musty, sour odor. The treated chips showed onlytraces of microbial growth, were of a somewhat yellowish color, and hadno sour odor.

Example 2 The effectiveness of the kraft green liquor treatment inpreventing loss of wood substance caused by wood rotting fungi was alsoinvestigated. A laboratory method was used to compare weight loss intreated and untreated chips after exposure to fungal attack. Red pinechips, frozen for storage shortly after chipping in the green condition,were used. The chips were screened, knotty or resinous pieces removed,and the remainder well mixed. The chips were then allowed to air dry atroom temperature for 3 days. Then they were conditioned at 80 F. and 70percent relative humidity for 1 Week. At the end of this period, samplesof chips were precisely weighed to about grams.

The sample chips were then rewetted by being subjected to a vacuum ofabout 29 inches of mercury for 20 minutes followed by flooding withdistilled water. After draining to remove the excess water, the sampleswere treated with various concentrations of green liquor. Treatment withthe green liquor consisted of dipping the chips for 1 minute in the testsolution. The chips were removed from the solution and allowed to drainfor 1 hour. They were then placed in incubation tubes, 12-inch longglass cylinders, plugged at the top with cotton, and at the bottom withrubber stopper containing a hole for drainage.

The cylinders filled with chips were then steamed for 30 minutes at 212F. When cool, half the samples were inoculated with a peniophora fungusand the other half with a mixture of a peniophora and a chrysosporiumfungus. Both inoculation organisms are species of the above genericgroups and are isolates of southern pine chips. Both are found capableof substantially degrading Wood.

Inoculation Was performed by asceptically scrapping the mycelium fromthe surface of a test tube culture. The mycelium and 75 milliliters ofsterile distilled water were blended in a Waring blender for 20 seconds.When using the mixture of organisms, to maintain comparable levels ofinoculation, half of the mycelium from each of the two test tubes wereused and blended together as above. The blended mixture was thenasceptically poured over the chips and allowed to drain through thestopper at the bottom of the cylinder.

The cylinders were then placed in an incubator and maintained at atemperature of 82 F. for 7 weeks. Then the chips were removed from eachof the cylinders, dried, conditioned, and weighed as at the test start,and the weight losses calculated. The results of the variousconcentrations of kraft grain liquor treatment are indicated in thefollowing table:

WEIGHT LOSS OF TREATED CHIPS Concentration of solution, percent WeightSodium Sodium Iuocu- Initial Final 2 loss, carbonate sulfide lant 1weight, g. Weight, g. percent 1 20. 09 18. 63 7. 8 2 20. 05 18. 17 9. 11 20. 10 17. 13. 0 2 20. 01 17. 61 12. 0 l .20. 00 19. 2. 8 2 20. 05 19.87 9 1 20. 05 20.08 2 2 20. 02- 19. 71 l. 6 l 20. 07 19. 83 l. 2 2-20.06 20. 25 l.0 1 20. 05 20. 00 2 2 20. 01 20. 05 2 1 l=SpecieS ofPeniophora; 2=Species of Pencophora and Chrysosporium.

2 Weight corrected for treating chemical.

3 Not treated.

Example 3 Untreated fresh aspen chips soaked in a solution containing0.77 percent sodium sulfide and 3.1 percent sodium carbonate were placedin tower simulators (see- Springer, E. L., and Zoch, L. L., A Simulatorof an Outside Chip Pile, 1'16-117, Tappi 53(1), 1970). The chemicalpickup of the wood chips was 0.36 pound of sodium sulfide and 1.38pounds of sodium carbonate per pounds of chip. The tower simulators are4 feet in diameter and 16 feet high cylinders insulated with 6 inches offiberglass insulation. Each simulator was fed with two tower volumes perday of water saturated air. Four bags of approximately 40 pounds each ofchips were placed in each tower. The moisture content of the chips ineach bag was determined. The chips in the bags were treated the same asthe loose chips in the tower. The bags were placed 5 feet below the topof the chip bed in each tower.

The towers were unloaded after 6 months and each bag was reweighed andthe moisture content determined. During the test period the outsidesurfaces of chip towers were maintained at ambient temperature. Theaverage ovendry wood substance loss of the untreated chips was 5percent. The wood substance loss of the green liquor treated chips was1.6 percent. The treatment thus greatly reduced the loss of woodsubstance. Approximately twothirds of the wood loss without treatmentwas preserved by the treatment.

Having thus disclosd our invention, We claim:

1. The process of limiting the effect of wood destroying fungi on woodchips by dipping or spraying the chips with a fungicidally effectiveamount of an aqueous mixture comprising .77 to 2.38 percent sodiumsulfide and 3.10 to 9.62 percent sodium carbonate.

References Cited GregoryUses and Applications of Chemicals and RelatedMaterials, 1939, Rheinhold Pub. Co., pp. 530-1, 558-9.

Hajny--Outside Storage of Pulpwood Chips, Tappi, Journal of theTechnical Assoc. of the Pulp and Paper Industry, vol. 49, No. 10, 1966,pp. 97a-105a.

Springer et al.Control of Pulp Chip Deterioration with Craft GreenLiquor, USDA Forest Service Paper #FPLllO, May 1969, pp. 1-5.

ALBERT T. MEYERS, Primary Examiner L. SCHENKMAN, Assistant Examiner US.Cl. X.R. 424-127

